The present invention relates to liquid crystal display devices, in particular, to a liquid crystal display device equipped with a view angle compensating unit between a liquid crystal layer and a polarization plate.
Due to the properties of thinness, light weight, and low power consumption, the liquid crystal display device is used in a wide variety of applications either outdoors or indoors such as mobile equipments including portable telephone and PDA (Portable Digital Assistants), industrial applications such as POS (Point of Sales) system, and TV display.
Generally, the liquid crystal display device using TN (Twisted Nematic) is mainly used, but black and white tends to reverse when seen from a direction other than from the front since the view angle is narrow, and visibility becomes unsatisfactory. Thus, to improve the view angle, a method of compensating view angle by using a film in which molecules having negative anisotropy such as discotic liquid crystals are oriented is known (e.g., patent documents 1 to 3 described later).
A VA (Vertical Alignment) method in which the liquid crystal molecules are oriented vertical to the substrate and the liquid crystal molecules are oriented in a direction parallel to the substrate by electric field for display, an IPS (In Plane Switching) method in which the liquid crystal molecules are homogenous oriented parallel to the substrate, and the liquid crystal molecules are rotated in a direction of substrate plane when voltage is applied in a lateral electric field direction for display, and the like have been proposed, but the structure is complicating and the yield lowers.
A method disclosed in Japanese Laid-Open Patent Publication No. 2-15237 (Pgs. 7-12, FIG. 2) (Patent document 1) is known as a method of realizing a wide view angle using the Twist Nematic (TN) liquid crystal. That is, a liquid crystal layer configured by liquid crystals having positive dielectric anisotropy, a first transparent substrate and a second transparent substrate for sandwiching the liquid crystal layer are provided, where transparent electrodes for applying voltage to the liquid crystal layer and orienting the liquid crystal molecules perpendicular to the transparent substrate are stacked on the liquid crystal layer side of the first transparent substrate and the second transparent substrate, an orientation film for orienting the liquid crystal molecules of the liquid crystal layer is stacked further on the liquid crystal layer side of the transparent electrodes, a first polarization plate and a second polarization plate are respectively arranged on the side opposite to the liquid crystal layer of the first transparent substrate and the second transparent substrate, and two anisotropic films are arranged such that the optical axes are orthogonal to each other in at least one of between the first transparent substrate and the first polarization plate or between the second transparent substrate and the second polarization plate. When such method is used, optical anisotropy does not arise in plane and negative anisotropy arise in a direction perpendicular to the film plane by arranging the two anisotropy films such that the optical axes are orthogonal to each other, and thus the phase difference in the diagonal direction that occurs when electric field is applied between the transparent electrodes and the liquid crystal molecules of the liquid crystal layer are oriented perpendicular to the transparent substrate can be compensated, thereby enlarging the view angle. However, the anisotropy of the phase difference that occurs by the rising direction of the liquid crystal cannot be compensated with such method, and obtaining a wide view angle has limitations.
Another method is a method disclosed in Japanese Laid-Open Patent Publication No. 2005-283612 (Pgs. 4-9, FIG. 1) (patent document 2). A liquid crystal cell is proposed including a first transparent substrate and a second transparent substrate, and a liquid crystal layer sandwiched between the first transparent substrate and the second transparent substrate, the liquid crystal layer being configured by Nematic liquid crystals that are anti-parallel oriented, transparent electrodes for applying voltage to the liquid crystal layer and orienting the liquid crystal molecules perpendicular to the transparent substrate being stacked on the liquid crystal side of the first transparent substrate and the second transparent substrate, a first polarization plate and a second polarization plate being respectively arranged on the side opposite to the liquid crystal layer of the first transparent substrate and the second transparent substrate, an optical compensation film being arranged in at least one of between the first transparent substrate and the first polarization plate or between the second transparent substrate and the second polarization plate, and an average orientation direction of the molecules of the optical compensation film being substantially parallel to the film surface, where the liquid crystal cell includes two or more pixels and has two or more regions in which the orientation state of the liquid crystal molecules of the liquid crystal layer of each pixel differ from each other in time of no voltage application and in time of voltage application. According to such configuration, although description is made that the average orientation of the molecules of the optical compensation film is substantially parallel to the film surface and that two or more regions in which the orientation state of the liquid crystal molecules differ from each other are provided, the anisotropy of the phase difference caused by the rising direction of the liquid crystal cannot be compensated in the relevant method of the example, similar to patent document 1.
Another further method is a method disclosed in Japanese Laid-Open Patent Publication No. 2005-010740 (Pgs. 5-8, FIG. 1) (patent document 3). The semi-transmissive liquid crystal display device of the relevant publication is configured by liquid crystal cells with a structure arranged with a transmissive region and a reflective region in the pixel, and includes a liquid crystal layer sandwiched between the first transparent substrate and the second transparent substrate, where transparent electrodes for applying voltage to the liquid crystal layer and orienting the liquid crystal molecules perpendicular to the transparent substrate are stacked on the liquid crystal layer side of the first transparent substrate and the second transparent substrate, and a first elliptical polarization plate and a second elliptical polarization plate are respectively arranged on the side opposite to the liquid crystal layer of the first transparent substrate and the second transparent substrate, and only the first elliptical polarization plate has a film in which hybrid orientation is fixed. In such configuration, the configuration becomes complicating since two elliptical polarization plates are used and optimization of wavelength dispersion of refractive index anisotropy of the elliptical polarization plate and wavelength dispersion of refractive index anisotropy of the liquid crystal layer becomes difficult as light passes through the elliptical polarization plate twice, whereby light leakage occurs in time of black display and the contrast lowers.